Helium in zircon crystals which are obtained from drilling into very deep granites. These crystals contain uranium which is radioactive and decays to lead. A by-product of this process is the formation of helium, a very light, inert gas which readily escapes from rock.
Surprising evolutionists, a significant amount of helium was present inside the zircons which is empirical evidence that these formations must be young. “https://answersingenesis.org/age-of-the-earth/6-helium-in-radioactive-rocks/
The results show that because of all the helium still in the zircons, these crystals (found in Precambrian granite) could not be older than approximately 5,680 years (+/- 2000) years.